The two stars had a series of steamy sex scenes in new TV mini-series "Catherine the Great" and Mirren admits Jason is one of the best fake lovers she's ever had the pleasure of acting alongside.
"What a beautiful guy to have those sorts of scenes with," Mirren tells Entertainment Tonight. "Jason is the most wonderful actor to work with. He's this great combination of very masculine but at the same time very generous and it's a lovely combination."
"I'd work with him again and again. I've only done it twice so far... We love each other."
Clarke, who plays Grigory Potemkin opposite the Oscar winner's Catherine, also teamed up with the British actress for horror movie "Winchester".
He admits he always has fun working with Mirren, because she's "very naughty", adding, "She's very cheeky, she's very alive and mischievous, so it's easy. The funny thing is, you're sitting there with Helen and you watch her in a close-up... and it's quite stunning what she does."
"We always laugh. We were being mischievous in some of the great palaces of Europe... Catherine and Potemkin, they were wonderful partners. It's a great relationship... They were an amazing couple."
"Catherine the Great" debuts on HBO on 21 October.