Cover - shares	3 Months Ended
	Mar. 31, 2026	May 15, 2026
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Amendment Flag	false
Document Period End Date	Mar. 31, 2026
Document Fiscal Year Focus	2026
Document Fiscal Period Focus	Q1
Entity Information [Line Items]
Entity Registrant Name	Twelve Seas Investment Co III/Cayman
Entity Central Index Key	0002052243
Entity File Number	001-43011
Entity Tax Identification Number	86-2888466
Entity Incorporation, State or Country Code	E9
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Shell Company	true
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Contact Personnel [Line Items]
Entity Address, Address Line One	2685 Nottingham Avenue
Entity Address, City or Town	Los Angeles
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	90027
Entity Phone Fax Numbers [Line Items]
City Area Code	(917)
Local Phone Number	361-1177
Units, each consisting of one Class A Ordinary Share and one Right
Entity Listings [Line Items]
Title of 12(b) Security	Units, each consisting of one Class A Ordinary Share and one Right
Trading Symbol	TWLVU
Security Exchange Name	NASDAQ
Class A Ordinary Shares, par value $0.0001 per share
Entity Listings [Line Items]
Title of 12(b) Security	Class A Ordinary Shares, par value $0.0001 per share
Trading Symbol	TWLV
Security Exchange Name	NASDAQ
Rights, each entitling the holder to receive one-tenth (1/10) of one Class A Ordinary Share
Entity Listings [Line Items]
Title of 12(b) Security	Rights, each entitling the holder to receive one-tenth (1/10) of one Class A Ordinary Share
Trading Symbol	TWLVR
Security Exchange Name	NASDAQ
Class A Ordinary Shares
Entity Listings [Line Items]
Entity Common Stock, Shares Outstanding		17,745,000
Class B Ordinary Shares
Entity Listings [Line Items]
Entity Common Stock, Shares Outstanding		5,692,500