It was indeed the Pullman London St. Pancras!
Awesome! You're staying at the Pullman London St Pancras
100-110 Euston Road, London, GB NW1 2AJ
Check-in: Fri, Mar 24 - 02:00pm
Check-out: Tue, Mar 28 - 12:00pm
Room: 1 room (1 king bed) | 2 adults | 1 child
Nights: 4 nights
Amenities: Free Internet, Smoke-free rooms, Fitness center, Restaurant(s), Business center, Internet access
Accessibility: Accessible path of travel, In-room accessibility, Accessible parking, Roll-in shower
$516.00 ($129.00 per night x 4 nights x 1 room)
Taxes & fees: $153.19
Promo code: -$30.00
Total (USD): $639.19
Best rate (also non-refundable) on Pullman's website was US$733.