See all posts by Rupert Hargreaves Don’t miss our special stock presentation.It contains details of a UK-listed company our Motley Fool UK analysts are extremely enthusiastic about.They think it’s offering an incredible opportunity to grow your wealth over the long term – at its current price – regardless of what happens in the wider market.That’s why they’re referring to it as the FTSE’s ‘double agent’.Because they believe it’s working both with the market… And against it.To find out why we think you should add it to your portfolio today… 4 FTSE 100 dividend stocks I reckon could explode in 2021! Most investors buy FTSE 100 dividend stocks expecting a steady return. The large-cap blue-chip stocks aren’t really known for their explosive capital growth.Indeed, they tend to be mature businesses which produce a steady stream of cash that can be returned to investors. Unfortunately, the trade-off here is that these companies don’t tend to achieve much in the way of earnings growth, which can hold back the performance of their shares. 5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…However, there are a handful of FTSE 100 dividend stocks I reckon could explode in value in 2021. FTSE 100 dividend stocksWhen it comes to FTSE 100 dividend stocks, two companies stand out in particular as being deeply undervalued at present. These are telecommunications giants Vodafone and BT. Granted, BT is no longer the dividend champion it once was. The company was forced to cut its payout earlier this year. Nevertheless, management is planning to restore the payout in the near term, and I think this could be a significant positive catalyst for the stock. Vodafone has maintained its dividend throughout the crisis. The yield currently stands at around 6.3%. But the company’s stock price doesn’t reflect this level of income. The shares continue to trade close to a multi-year low. The same is true of shares in BT. I think this is unwarranted. These FTSE 100 dividend stocks have fared better than most in the pandemic, as they’ve continued to provide vital services for their customers. I think the market has overlooked this fact, but this could change in 2021 as the recovery begins. And when it does, I reckon shares in Vodafone and BT could explode higher as investors rush to buy back into these two defensive income stocks while they trade at depressed levels. Blue-chip incomeInvestors also seem to have been avoiding shares in GlaxoSmithKline. This company has suffered a drop in sales this year as global vaccination programmes were postponed at the height of the pandemic. The programmes may have been delayed, but they haven’t been eliminated forever. They should resume next year when the world returns to some sort of normality.That suggests to me Glaxo’s earnings and sales could jump next year. And that may lead to a substantial increase in the company’s stock price. In the meantime, shares in the pharmaceutical giant currently support a dividend yield of around 4.5%. HSBC used to be one of the most sought-after FTSE 100 dividend stocks. Unfortunately, the lender was banned from paying dividends to investors by regulators earlier this year. That was the right decision at the time. Regulators have now declared banks can resume dividends in the new year.I reckon HSBC will jump at the chance to make a distribution because management was already pushing for a change in the rules. And when the company resumes payouts, I reckon the stock will jump substantially from current levels, building on a substantial rally that’s taken place over the past few months. City analysts have pencilled in a potential dividend yield of 5.5% for next year. Enter Your Email Address Image source: Getty Images There’s a ‘double agent’ hiding in the FTSE… we recommend you buy it! Rupert Hargreaves owns no share mentioned. The Motley Fool UK has recommended GlaxoSmithKline and HSBC Holdings. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors. Simply click below to discover how you can take advantage of this. Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. Our 6 ‘Best Buys Now’ Shares Rupert Hargreaves | Saturday, 19th December, 2020 I would like to receive emails from you about product information and offers from The Fool and its business partners. Each of these emails will provide a link to unsubscribe from future emails. More information about how The Fool collects, stores, and handles personal data is available in its Privacy Statement. Click here to get access to our presentation, and learn how to get the name of this ‘double agent’!