Die-hard republican Jeremy Corbyn is no stranger to criticism when it comes to the royal family. He was lambasted last year for failing to sing the national anthem at a Battle of Britain memorial service, and over whether he knelt in front of the monarch when he was sworn into the Privy Council.
But despite all this, Corbyn has confirmed he does intend to send the Queen his regards on her birthday - in fact, he is "looking forward" to it.
The issue was raised at PMQs by the Tory MP Nigel Adams (Selby and Ainsty) ahead of a celebratory debate in the House of Commons.
David Cameron replied to Adams: "I'm very glad you have raised this. I will certainly pass on his best wishes and best wishes from right across Yorkshire.
"Tomorrow is an important landmark, not only for Her Majesty the Queen but also for our country and for the Commonwealth as a whole.
"She has served our nation with such dignity, with such ability for so many years, 64 years on the throne, and I think it's right we are going to have the opportunity in the House tomorrow to pay tribute to what she has done.
"I know the whole country and the whole House will want to join me in saying long may she reign over us."
Corbyn, rising to ask his first question of the session, then said: "I am also looking forward to wishing her a happy birthday tomorrow."
But his remark prompted laughter across the House and mixed opinions across Twitter.
How embarrassing was Jeremy Corbyn's line abouth the Queen's birthday at #PMQs .?
-- Jamie Sheehan (@JamieSheehan79) April 20, 2016
@adamboultonSKY Cynical sounding birthday greeting to the Queen from Corbyn - the anti royalist!!
-- Viv Jones (@vivjones10) April 20, 2016
Jeremy Corbyn pretends he's looking forward to wishing the Queen happy birthday tomorrow. Cos you have to. #PMQs
-- David Singleton (@singersz) April 20, 2016